This invention relates to alkanolamine corrosion inhibiting compositions containing bismuth salts for use in stainless steel acid gas removal equipment and methods for their use.
It is well known from the prior art that acid gases such as carbon dioxide, hydrogen sulfide and carbonyl sulfide can be removed from gaseous feed streams such as natural gas and synthesis gas using dilute aqueous solutions of potassium carbonate, alkanolamines such as monoethanolamine, diethanolamine, and methyl diethanolamine, and other weak bases. The usual procedure is to use a contactor wherein the absorbent solution contacts the feed stream and to use a regenerator with a reboiler wherein the rich absorbent containing the acid gas components is regenerated back to the free absorbent. The solution is then recycled back to the contactor for reuse.
There has been much activity devoted to solving the problem of metallic corrosion in the equipment used in the above process.
It is common practice to use stainless steel and nickel alloys in sensitive areas such as heat exchange equipment, regenerator trays and absorber trays.
U.S. Pat. No. 3,087,778 (4-30-63) provides for inhibition of potassium carbonate solutions by using 1,000 to 5,000 p.p.m. of the trivalent oxides of arsenic, antimony or bismuth.
U.S. Pat. No. 3,808,140 (4-30-74) provides for inhibition of alkanolamine solutions by using minor amounts of vanadium and antimony compounds.
U.S. Pat. No. 3,896,044 (7-22-75) provides for inhibition of alkanolamine solutions by using minor amounts of nitro substituted aromatic acids or salts thereof.
U.S. Pat. No. 3,959,170 (5-25-76) provides for inhibition of alkanolamine solutions using a minor amount of a stannous salt.
U.S. Pat. No. 4,071,470 (1-31-78) provides for inhibition of alkanolamine solutions using a minor amount of the reaction product of copper, sulfur, and an alkanolamine.
U.S. Pat. No. 4,096,085 (6-20-78) provides for inhibition of alkanolamine solutions using minor amounts of a polyamine, with or without copper, and sulfur.
U.S. Pat. No. 4,100,099 (7-11-78) provides for inhibition of sour gas conditioning fluids using minor amounts of quaternary pyridinium salts and alkylene polyamines.
U.S. Pat. No. 4,100,100 (7-11-78) provides for inhibition of sour gas conditioning fluids using minor amounts of quaternary pyridinium salts, thiocyanate compounds or thioamide compounds, and divalent cobalt compounds.
U.S. Pat. No. 4,102,804 (7-25-78) provides for inhibition of sour gas conditioning solutions using minor amounts of a quaternary pyridinium salt, and a thiocyanate compound, a sulfide compound or a thioamide compound.
U.S. Pat. No. 4,116,629 (9-26-78) provides for the corrosion inhibition of stainless steels (types 410 and 430) when in contact with carbonate solutions by using nickel salts.
U.S. Pat. No. 4,143,119 (3-6-79) provides for inhibition of sour gas conditioning solutions using minor amounts of copper and a polysulfide generated in situ.
While the above compositions are effective, they each have various defects which detract from their universal use. For example, compounds of arsenic, antimony and vanadium are known to be toxic and their use presents waste disposal problems for the plant operators. The use of the quaternary pyridinium compounds are known to cause a foaming problem in certain instances.